This invention relates to semiconductor devices and more specifically relates to a structure and process to improve the threshold voltage stability of a MOSgated device under high temperature reverse bias.
The threshold voltage (Vth) of MOSgated devices has been found to shift under high temperature reverse bias (HTRB).
More specifically, a Vth shift of about (xe2x88x92) 1 volt has been found after about 500 to 1000 hours HTRB.
It is believed that this is caused by sodium ions in the field oxide which drift laterally and accumulate at the edge of the channel in the first active cell or stripe.
In accordance with the present invention, a cut is made in the P+ oxide layer to eliminate an Na+ diffusion path. This cut has been found to substantially stabilize Vth in HTRB up to 1000 hours.